1. Field of the Invention
The present invention relates to a prepreg, a circuit board, and a method for manufacturing the prepreg and the circuit board.
2. Description of the Related Art
In recent years, with a trend toward compact lightweight high-performance electronic equipment, there has been a growing demand for low-cost multilayer circuit boards that can achieve high-density mounting of semiconductor chips such as LSIs in the field of home electronic applications. To meet this market demand, the technology has been developed to make resin multilayer circuit boards, which can be supplied at lower cost, suitable for high-density mounting, instead of conventionally mainstream ceramic multilayer circuit boards. Examples of such resin multilayer circuit boards include a circuit board having an Interstitial Via Hole (hereinafter, referred to as IVH) structure in all layers, as disclosed in JP 6(1994)-268345 A.
A resin multilayer circuit board having the IVH structure in all layers uses a composite material, including a nonwoven aramid reinforcing material and an epoxy resin, as an insulating layer. This circuit board adopts an IVH connection between layers, with which any wiring pattern layers can be connected electrically at desired positions through a conductive paste. Thus, the resin multilayer circuit board characterized by the IVH structure in all layers is relatively inexpensive and suitable for high-density mounting.
The above conventional technique requires a prepreg obtained by impregnating the nonwoven aramid reinforcing material with the epoxy resin while leaving a hollow inside. That is, the conventional technique cannot be realized unless a specific material is used. However, there is a wide variety of circuit boards the market demands, e.g., a circuit board that has a low dielectric constant and is suitable for high-speed transmission or a circuit board that can achieve both high-density mounting and high heat resistance, in addition to a circuit board that enables high-density mounting. Thus, it is necessary to provide a circuit board suitable for high-density mounting by using any materials with desired physical properties.